Recently, production of urethane bampers or the like in a mold by means of reactive injection molding is being watched with keen interest and various proposals have been made as stated, for example, in U.S. Pat. No. 4,254,069: ibid 3,838,076, ibid 4,216,543: ibid 4,246,363: ibid 4,269,945 and the like.
In this area, a specifically attractive one is the method of Japanese Patent Publication (unexamined) 188643/83, wherein a mixture of end-amine bearing polyethers having an average molecular weight of 1,500 or more, end-amine bearing chain extender and polyisocyanate is reacted in a closed mold to give an elastic polyurea injection-molding which is excellent in mechanical strength, heat resistance and other desired properties.
Recently, as an automobile decorative material, various plastics have been examined and some are actually used in certain areas.
Since a polyurethane molding obtained by the reaction of polyalkylene polyol and polyisocyanate in a mold has many problems such that polyurethane is rather poor in heat resistance, is expensive and has certain limits in its coating, public interests are prone to move, from polyurethane/polyurea, to polyurea which has excellent heat resistance.
However, the reaction speed between an end-amine bearing polyether and polyisocyanate is much higher than the reaction speed between a polyether polyol and polyisocyanate, and therefore, in the case of such polyurea molding, the reaction mixture must be filled in a mold within a very short period of time, say 1 second or less.
This, in turn, may give rise to certain difficulties in both respects of apparatus and materials to be used.
That is, there are problems of efficient control in the optimum speed and in the viscosity of the injected material.
The principal object of substituting polyurea for polyurethane in an automobile exterior panel is to simplify the automobile production line by enabling the simultaneous application and baking the enamel on the assembly for both steel and plastic components.
Therefore, such molding should preferably well withstand any thermal deformation at the baking temperature in an electro-deposition coating line.
However, polyurea materials with excellent heat resistance properties tend to be more brittle than polyurethane, and therefore, have a lower impact resistance.
Therefore, an essential feature of the work is the development of a new reactive injection molding resinous composition that will give both excellent heat resistance and impact resistance.